Disk drives are apparatus comprising one or more substantially thin, magnetic disks that are rotated by a spindle motor that is responsive to the drive's control mechanism and associated electronics that communicate data via read and write heads. The disk drives are used in computer systems, such as personal computers, laptop computers and workstation equipped with computer systems, to store large amounts of data, (giga-byte range), in a form that is machine readable for subsequent use by a user. The magnetic disk comprises a surface of magnetizable material having a number of annular regions, called tracks, that extend circumferentially around the disk. Each track is divided into blocks called sectors. Data and other identification information is stored in the sectors in the form of magnetic transitions. The reading and writing of data is accomplished by read and write heads that are positioned on the required track by the drive's positioning control system. Commonly used are magneto-resistive heads having a read element and a write element, such as illustrated in FIGS. 3 and 6. Because the physical act of placing the read/write head over the required track for performing the read and write operations is not done with 100% accuracy, a track misregistration (tmr) budget is generally employed. The track misregistration budget sets a threshold for determining a distance, by example in micro-inches, by which the drive's head can go off-track prior to generating a write inhibit signal that activates the drive's write inhibit circuit that disables further read/write operations. The prior art teaches that the track misregistration budget, hence the write inhibit threshold, is based on the nominal track spacing without any consideration that the actual track spacing on the particular magnetic disk installed in the disk drive may in fact be greater, or lesser than the nominal track spacing, which is a generalized design value based on a population of disks for a particular disk drive product. The use of the nominal track spacing results in needless disk drive fallout where in fact the actual track spacing is wider than the nominal track spacing value. To applicant's knowledge disk drive write inhibit circuitry has not been enabled based on actual disk track spacing, which, if wider than a nominal design track spacing, will reduce fallout due to servo off-track conditions and decrease write inhibit events for improved disk drive performance.
Thus, a need is seen to exist for a disk drive having a write inhibit threshold that is adapted in accordance with the disk drive's actual data track spacing and which controls the generation of a write inhibit signals such that a reduction in fallout due to servo off-track conditions results, and such that a decrease in write inhibit events also result for improving a disk drive's performance.
It is therefore a primary object of the present invention to provide a disk drive having a write inhibit threshold that is adapted in accordance with the disk drive's actual data track spacing and which controls the generation of a write inhibit signals such that a reduction in fallout due to servo off-track conditions occurs, and such that a decrease in write inhibit events result for improving a disk drive's performance.